Method for estimating drive torque of variable displacement compressor and system for controlling drive source rotation speed

ABSTRACT

The value of an estimated drive torque is prevented from greatly differing from an actual drive torque of a variable displacement compressor immediately after a refrigerating cycle is started. A first estimated drive torque that is calculated based on a physical quantity other than the pressure of a refrigerant and increases with lapse of time after the variable displacement compressor begins to compress the refrigerant and a second estimated drive torque calculated using the pressure of the refrigerant are compared and the one with the value closer to the actual drive torque is employed as an estimated drive torque of the variable displacement compressor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for estimating a drive torqueof a variable displacement compressor used to drive a refrigeratingcycle and a system for controlling a rotation speed of a drive sourcefor driving a variable displacement compressor and, more particularly,is suitable for an air conditioner for a vehicle.

2. Description of the Related Art

Conventionally, the drive torque of a variable displacement compressorused for driving a refrigerating cycle is estimated using the pressureon the high-pressure side of the refrigerating cycle (for an example,see Patent document 1).

However, there has been a problem that, if the drive torque is estimatedusing the pressure etc. on the high-pressure side of a refrigeratingcycle in a transient state immediately after the refrigerating cycle isstarted, the estimated drive torque greatly differs from an actual drivetorque.

Further, there has been another problem that when a variabledisplacement compressor is driven by an engine, which is a drive source,if a target rotation speed of the engine is determined based on anestimated drive torque greatly differing from the actual drive torqueduring the period of engine idling, it is not possible to harmonize withthe control of other devices driven by the engine and, therefore, thetarget rotation speed of the engine does not stabilize.

[Patent document 1]

Japanese Unexamined Patent Publication (Kokai) No. 2001-180261

SUMMARY OF THE INVENTION

The present invention has been developed to solve the above-mentionedproblems and the object thereof is to prevent the value of an estimateddrive torque from greatly differing from the actual drive torque of avariable displacement compressor immediately after a refrigerating cycleis started.

In order to attain the above-mentioned object, in a first aspect of thepresent invention, a refrigerating cycle comprises: a variabledisplacement compressor having a compression mechanism section forcompressing a refrigerant and a displacement variable mechanism forvarying the displacement of the refrigerant to be compressed by thecompression mechanism section; a condenser for condensing therefrigerant compressed by the variable displacement compressor; apressure reducing means for reducing the pressure of the refrigerantcondensed by the condenser; an evaporator for evaporating therefrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means, and the evaporator; and apressure detection means for detecting the pressure of the refrigerantfrom the variable displacement compressor to the pressure reducingmeans. In the refrigerating cycle, a method for estimating a drivetorque of the variable displacement compressor comprises: a first drivetorque estimation means for calculating a first estimated drive torqueof the variable displacement compressor, which is calculated based on atleast a physical quantity other than the pressure of the refrigerantdetected by the pressure detection means and gradually increases withlapse of time after the variable displacement compressor begins tocompress the refrigerant; and a second drive torque estimation means forcalculating a second estimated drive torque of the variable displacementcompressor using the pressure of the refrigerant detected by thepressure detection means, wherein the first estimated drive torque andthe second estimated drive torque are compared and the one with thelower value is employed as an estimated drive torque of the variabledisplacement compressor.

Due to this, even if the second drive torque estimation means calculatesa second estimated drive torque greater than the actual drive torqueusing the pressure of the refrigerant immediately after therefrigerating cycle starts to operate, a first estimated drive torquecalculated by the first drive torque estimation means for calculating anestimated drive torque based on a physical quantity other than thepressure of the refrigerant gradually increases with lapse of time afterthe variable displacement compressor begins to compress the refrigerant.Therefore, it will be less than the above-mentioned second estimateddrive torque during the period of transient immediately after therefrigerating cycle is started, that is, when the variable displacementcompressor begins to discharge the refrigerant. As a result, the firstestimated drive torque is employed as an estimated drive torque and,therefore, it is possible to prevent the estimated drive torque fromgreatly differing from the actual drive torque of the variabledisplacement compressor immediately after the refrigerating cycle isstarted.

In a second aspect of the present invention, a refrigerating cyclecomprises: a variable displacement compressor having a compressionmechanism section for compressing a refrigerant and a displacementvariable mechanism for varying the displacement of the refrigerant to becompressed by the compression mechanism section; a condenser forcondensing the refrigerant compressed by the variable displacementcompressor; a pressure reducing means for reducing the pressure of therefrigerant condensed by the condenser; an evaporator for evaporatingthe refrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means, and the evaporator; and apressure detection means for detecting the pressure of the refrigerantfrom the variable displacement compressor to the pressure reducingmeans. In the refrigerating cycle, a method for estimating a drivetorque of the variable displacement compressor comprises: a first drivetorque estimation means for calculating a first estimated drive torqueof the variable displacement compressor based on at least a physicalquantity other than the pressure of the refrigerant detected by thepressure detection means; a second drive torque estimation means forcalculating a second estimated drive torque of the variable displacementcompressor using the pressure of the refrigerant detected by thepressure detection means; and a lapse of time measurement means formeasuring the lapse of time after the variable displacement compressorbegins to compress the refrigerant are provided wherein, when the lapseof time measured by the lapse of time measurement means is less than apredetermined time, the first estimated drive torque is employed as anestimated drive torque of the variable displacement compressor and whenthe lapse of time measured by the lapse of time measurement means isequal to or more than the predetermined time, the second estimated drivetorque is employed as an estimated drive torque of the variabledisplacement compressor.

Due to this, when the lapse of time, after the refrigerating cycle isstarted, is less than the predetermined time, the first estimated drivetorque is employed as an estimated drive torque and, therefore, it ispossible to prevent the estimated drive torque from greatly differingfrom the actual drive torque of the variable displacement compressorimmediately after the refrigerating cycle is started.

A third aspect of the present invention according to the above-mentionedsecond aspect is characterized in that the displacement variablemechanism varies the displacement of the refrigerant to be compressed bythe compression mechanism section by a control current input from theoutside and that the first drive torque estimation means calculates thefirst estimated drive torque based on the control current.

Due to this, the first drive torque estimation means calculates thefirst estimated drive torque based on the volume of refrigerant to becompressed by the variable displacement compressor and, therefore, it ispossible to more accurately calculate the first estimated drive torque.

A fourth aspect of the present invention according to theabove-mentioned first or second aspect is characterized in that thefirst drive torque estimation means calculates the first estimated drivetorque using the lapse of time after the variable displacementcompressor begins to compress the refrigerant and the value stored inadvance in accordance with the lapse of time. Due to this, it becomespossible to quickly calculate the first estimated torque.

A fifth aspect of the present invention is characterized in that thevariable displacement compressor is driven by a drive source and theestimated drive torque calculated by the method for estimating a drivetorque of a variable displacement compressor described in any one of thefirst to fourth aspects is used to control the rotation speed of thedrive source.

Due to this, it is possible to optimize the rotation speed of the drivesource by using the estimated drive torque, calculated so as not togreatly differ from the actual drive torque, to control the rotationspeed of the drive source.

A sixth aspect of the present invention comprises a refrigerating cyclehaving a variable displacement compressor having a compression mechanismsection for compressing a refrigerant and a displacement variablemechanism for varying the displacement of the refrigerant to becompressed by the compression mechanism section; a condenser forcondensing the refrigerant compressed by the variable displacementcompressor; a pressure reducing means for reducing the pressure of therefrigerant condensed by the condenser; an evaporator for evaporatingthe refrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means, and the evaporator; and apressure detection means for detecting the pressure of the refrigerantfrom the variable displacement compressor to the pressure reducingmeans, a drive source for driving the variable displacement compressor,a lapse of time measurement means for measuring the lapse of time afterthe variable displacement compressor begins to compress the refrigerant,a drive torque estimation means for calculating an estimated drivetorque of the variable displacement compressor using the pressure of therefrigerant detected by the pressure detection means, and a rotationspeed calculation means for calculating a target rotation speed of thedrive source using the estimated drive torque are provided, and ischaracterized in that, when the lapse of time measured by the lapse oftime measurement means is less than a predetermined time, a value, whichis an obtained by subtracting a torque calculated by a predeterminedcalculation from an estimated drive torque calculated by the drivetorque estimation means, is used as an estimated drive torque to be usedin calculation, and the estimated drive torque calculated by the drivetorque estimation means is used as it is in calculation when the lapseof time measured by the lapse of time measurement means is equal to ormore than the predetermined time.

Due to this, it becomes possible to optimize the control of the drivesource rotation speed by the single drive torque estimation means.

A seventh aspect of the present invention according to the fifth orsixth aspect is characterized in that the rotation speed calculationmeans calculates a target idle rotation speed of the drive source.

Due to this, it is possible to reduce idling noises and improve the fuelconsumption efficiency of the drive source by optimizing the targetidling rotation speed.

In an eighth aspect of the present invention, a refrigerating cyclecomprises: a variable displacement compressor having a compressionmechanism section for compressing a refrigerant and a displacementvariable mechanism for varying the displacement of the refrigerant to becompressed by the compression mechanism section; a condenser forcondensing the refrigerant compressed by the variable displacementcompressor; a pressure reducing means for reducing the pressure of therefrigerant condensed by the condenser; an evaporator for evaporatingthe refrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means, and the evaporator; and apressure detection means for detecting the pressure of the refrigerantfrom the variable displacement compressor to the pressure reducingmeans. In the refrigerating cycle, a method for estimating a drivetorque of a variable displacement compressor comprises: a first drivetorque estimation means for calculating a first estimated drive torqueof the variable displacement compressor, which is calculated based on atleast a physical quantity other than the pressure of the refrigerantdetected by the pressure detection means and gradually increases withlapse of time after the variable displacement compressor begins tocompress the refrigerant; and a second drive torque estimation means forcalculating a second estimated drive torque of the variable displacementcompressor using the pressure of the refrigerant detected by thepressure detection means, wherein the first estimated drive torque andthe second estimated drive torque are compared and the one with thevalue closer to the actual drive torque is employed as an estimateddrive torque of the variable displacement compressor. Due to this, thesame effect as that in the first aspect can be obtained.

The present invention may be more fully understood from the descriptionof the preferred embodiments of the invention set forth below, togetherwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagram showing a configuration in an embodiment of thepresent invention.

FIG. 2 is a graph showing the drive torque of a variable displacementcompressor 1 with respect to the lapse of time in the embodiment of thepresent invention.

FIG. 3 is a flow chart showing a method for determining an estimatedtorque in the embodiment of the present invention.

FIG. 4 is a graph showing the drive torque variation with respect to thelapse of time when the variable displacement compressor 1 varies thedischarge displacement in an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments

Embodiments of the present invention are explained below. FIG. 1 isdiagram showing a connection relationship of a refrigerating cycle Rchaving a variable displacement compressor 1 driven by an engine, notshown, through a belt, an ECU 2 for controlling the refrigerating cycleRc and the engine, and a sensor group (8 to 12), to be described later,relating to input and output of the ECU 2.

The variable displacement compressor 1 which is a widely known,comprises a compression mechanism section for compressing a refrigerantand a displacement variable mechanism for varying the displacement inwhich the refrigerant is compressed by the compression mechanism sectionand the displacement variable mechanism is controlled by a displacementcontrol signal input from the ECU 2.

The refrigerating cycle Rc comprises the above-mentioned variabledisplacement compressor 1, a condenser 3 for condensing a refrigerantcompressed by the variable displacement compressor 1, a gas-liquidseparator 4 for separating the refrigerant condensed by the condenser 3into gas and liquid, an expansion valve 5, which is a pressure reducingmeans, for reducing in pressure the liquid refrigerant separated by thegas-liquid separator 4, an evaporator 6 for evaporating the refrigerantreduced in pressure by the expansion valve 5, and a refrigerant pipe 7for connecting the variable displacement compressor 1, the condenser 3,the gas-liquid separator 4, the expansion valve 5, and the evaporator 6,and further comprises a high pressure sensor 8 for detecting thepressure of the refrigerant from the variable displacement compressor 1to the expansion valve 5. The expansion valve 5 is a thermostaticexpansion valve for reducing the pressure of the liquid refrigerantseparated by the gas-liquid separator 4 by setting an opening of thevalve in accordance with the pressure of a gas in atemperature-sensitive cylinder 5 a arranged downstream of the evaporator6 so as to expand the liquid refrigerant.

To the ECU 2, a high pressure signal detected by the above-mentionedhigh pressure sensor 8, an inside air temperature signal from an insideair temperature sensor 9 for detecting the temperature in a vehiclecompartment space of a vehicle, not shown, an outside air temperaturesignal from an outside air temperature sensor 10 for detecting thetemperature at the outside of the vehicle, a solar radiation signal froma solar radiation sensor 11 for detecting the quantity of solarradiation that comes into the vehicle compartment, and an evaporatortemperature signal from an evaporator temperature sensor 12 attached tothe surface of the evaporator 6 for detecting the temperature of theevaporator 6 are input via an A-D converter 13. To the ECU 2, an enginerotation speed signal from an engine rotation speed detection means 14for detecting the rotation speed of an engine, an air conditioner ON/OFFsignal issued when a passenger operates an air conditioner operationpanel 15 arranged in the vehicle compartment, and an IG signal from anIG switch 17 for controlling conduction of a current to avehicle-mounted battery 16 are also input.

Then, the ECU 2 controls the displacement variable mechanism of thevariable displacement compressor 1, a condenser fan 18, an airconditioner blower fan 19, and the opening of an idle adjustment valve20 based on the above-mentioned signal group.

Here, the idle adjustment valve 20 is provided to a bypass pipe path 23that bypasses a throttle valve 22 arranged in an engine air-suction pipe21. During the period of engine idling, the ECU 2 adjusts the idlingrotation speed by adjusting the flow rate of the sucked air to besupplied to the engine by controlling the opening degree of the idleadjustment valve 20.

The optimum idle rotation speed during the period of engine idlingdiffers depending on the drive torque of an auxiliary device driven bythe engine through a belt and, therefore, the ECU 2 determines a targetidle rotation speed by estimating the drive torque of the variabledisplacement compressor 1 and determines an opening of the idleadjustment valve 20 based on the idle rotation speed.

A method for estimating the drive torque of the variable displacementcompressor 1 is explained below using FIG. 2 and FIG. 3. FIG. 2 is agraph showing the drive torque variation of the variable displacementcompressor 1 with respect to time in the present embodiment, in whichgraph the time is assumed to be to when an air conditioner ON signal isinput to the ECU 2 from the operation panel 15 and the variabledisplacement compressor 1 begins to be driven. In FIG. 2, the solid lineindicates the actual drive torque, the broken line indicates the firstestimated drive torque (TrqA) calculated based on a physical quantityother than the pressure on the high-pressure side of the refrigeratingcycle by the first drive torque estimation means according to thepresent invention, and the alternating long and short dashed lineindicates the second estimated drive torque (TrqB) calculated using thepressure on the high-pressure side of the refrigerating cycle by thesecond drive torque estimation means according to the present invention.The first estimated torque (TrqA) in the present embodiment isrepresented by a line that is an approximation of the drive torquevariation of the variable displacement compressor 1 with respect to timeand this line shows that the drive torque monotonically increases withthe lapse of time after the air conditioner ON/OFF signal is input.

FIG. 3 is a flow chart for determining which estimated drive torque touse to control the engine rotation speed between the above-mentionedfirst estimated drive torque (TrqA) and the second estimated drivetorque (TrqB) in the ECU 2 in the present embodiment.

First, in step S1, the above-mentioned high pressure signal and theengine rotation speed are read and then the flow proceeds to step S2.

In step S2, the first estimated drive torque (TrqA) is calculated basedon the map stored in advance in the ECU 2, without using the highpressure signal and then the flow proceeds to step S3. The map stores arelationship between the lapse of time after the air conditioner ON/OFFsignal is input and the above-mentioned first estimated drive torque(TrqA).

In step S3, the second estimated drive torque (TrqB) is calculated basedon the high pressure signal, the engine rotation speed signal, and thecontrol current value calculated by the ECU 2 for controlling theabove-mentioned displacement variable mechanism, and then the flowproceeds to step S4.

In step S4, the first estimated drive torque (TrqA) calculated in stepS2 is compared with the second estimated drive torque (TrqB) calculatedin step S3 and when the first estimated drive torque (TrqA) is less thanthe second estimated drive torque (TrqB), the flow proceeds to step S5and when the first estimated drive torque (TrqA) is greater than thesecond estimated drive torque (TrqB), the flow proceeds to step S6.

In step S5, a target idling rotation speed during the period of engineidling is determined based on the first estimated drive torque (TrqA)and then the flow proceeds to step S7.

In step S6, a target idling rotation speed during the period of engineidling is determined based on the second estimated drive torque (TrqB)and then the flow proceeds to step S7.

In step S7, the flow returns to step S1.

Next, the effect of the present embodiment is explained. In the presentembodiment, the first estimated drive torque (TrqA) that increases withlapse of time after the air conditioner ON/OFF signal is input and thesecond estimated drive torque (TrqB) calculated based on the highpressure signal, the engine rotation speed signal, and the controlcurrent value of the displacement variable mechanism are compared, andthe target idle rotation speed is determined based on the smallerestimated drive torque. Therefore, even immediately after the airconditioner ON/OFF signal is input, the second estimated drive torque(TrqB), that is calculated based on the high pressure signal and isgreater than the actual one, is not used, but the first estimated drivetorque (TrqA) that increases with lapse of time is used. Due to this, itis possible to determine the target idle rotation speed by using theestimated drive torque close to the actual drive torque of the variabledisplacement compressor 1, as shown in FIG. 2.

Due to this, it is possible to optimize the target idle rotation speedof an engine and therefore, the idling noise can be reduced and theengine fuel consumption efficiency can be improved.

In the present embodiment, the first estimated drive torque (TrqA) iscalculated based on the map stored in advance in the ECU 2. However, asshown in FIG. 4, even if the volume of refrigerant that the variabledisplacement compressor 1 compresses is varied by the displacementvariable mechanism, it is unlikely that the actual drive torque variesconsiderably depending on the volume of refrigerant to be compressed(hereinafter, referred to as a discharge displacement) immediately afterthe air conditioner ON/OFF signal is input and, therefore, it ispossible to use the same single map regardless of the volume ofrefrigerant to be compressed. As is also obvious from FIG. 4, the periodof time (T0 to T1, T0 to T2, T0 to T3) during which a target idlerotation speed is determined using the first estimated drive torque(TrqA) is lengthened depending on the change in discharge displacement.

Other Embodiments

In the present embodiment, the first estimated drive torque (TrqA) iscalculated based on the map of the estimated torque that is stored inadvance in the ECU 2 and which rectilinearly increases with lapse oftime after the air conditioner ON/OFF signal is input. However, thepresent invention is not limited to this, and it may be calculated byany method provided the first estimated drive torque (TrqA) iscalculated without using the high pressure signal, and the firstestimated drive torque (TrqA) may be calculated based on the controlcurrent value of the displacement variable mechanism. Due to this, it ispossible to more accurately calculate the first estimated drive torque(TrqA).

Further, in the above-mentioned embodiment, which one of the firstestimated drive torque (TrqA) and the second estimated drive torque(TrqB) is used is determined depending on the magnitude of the firstestimated drive torque (TrqA) and the second estimated drive torque(TrqB), however, the present invention is not limited to this, and whichone of the first estimated drive torque (TrqA) and the second estimateddrive torque (TrqB) is used may be determined based on the lapse of timemeasured by a lapse of time measurement means provided for measuring thelapse of time after the air conditioner ON/OFF signal is input.Alternatively, it may also be possible to use the first estimated drivetorque (TrqA) until a predetermined time elapses after the airconditioner ON/OFF signal is input and then use the second estimateddrive torque (TrqB) after the predetermined time elapses.

Furthermore, in the above-mentioned embodiment, the optimum target idlerotation speed is determined while preventing the estimated drive torquefrom greatly differing from the actual drive torque by providing pluraldrive torque estimation means, however, the present invention is notlimited to this. It may also be possible to determine a target idlerotation speed by using a single drive torque estimation means forcalculating an estimated drive torque based on the high pressure signal,by including the above-mentioned lapse of time measurement means, and byusing a value, which is obtained by subtracting the torque calculated bya predetermined calculation from the estimated drive torque calculatedby the drive torque estimation means, until a predetermined timeelapses.

The high-pressure sensor 8 may be installed at any place provided thatit can detect the pressure of the refrigerant from the variabledisplacement compressor 1 to the expansion valve 5 and it may beinstalled to the main body of the variable displacement compressor 1 orit may be installed to the refrigerant pipe 7.

In the above-mentioned embodiment, a single map is used in order tocalculate the first estimated drive torque, however, the presentinvention is not limited to this, and plural maps may be used.

In the above-mentioned embodiment, the first estimated drive torque andthe second estimated drive torque are compared and the one with thesmaller value is employed as an estimated drive torque of the variabledisplacement compressor, however, the present invention is not limitedto this, and it may also be possible to compare the first estimateddrive torque and the second estimated drive torque and employ the onewith the value closer to the actual drive torque as an estimated drivetorque of the variable displacement compressor.

While the invention has been described by reference to specificembodiments chosen for the purposes of illustration, it should beapparent that numerous modifications could be made thereto, by thoseskilled in the art, without departing from the basic concept and scopeof the invention.

1. A method for estimating a drive torque of a variable displacementcompressor included in a refrigerating cycle, wherein the refrigeratingcycle comprises: a variable displacement compressor having a compressionmechanism section for compressing a refrigerant and a displacementvariable mechanism for varying a displacement of the refrigerant to becompressed by the compression mechanism section; a condenser forcondensing the refrigerant compressed by the variable displacementcompressor; a pressure reducing means for reducing pressure of therefrigerant condensed by the condenser; an evaporator for evaporatingthe refrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means, and the evaporator; and apressure detection means for detecting pressure of the refrigerant fromthe variable displacement compressor to the pressure reducing means, andwherein the method comprises: a first drive torque estimation means forcalculating a first estimated drive torque of the variable displacementcompressor, which is calculated based on at least a physical quantityother than pressure of refrigerant detected by the pressure detectionmeans and which gradually increases with lapse of time after thevariable displacement compressor begins to compress the refrigerant; anda second drive torque estimation means for calculating a secondestimated drive torque of the variable displacement compressor usingpressure of refrigerant detected by the pressure detection means, andthe first estimated drive torque and the second estimated drive torqueare compared and the one with the lower value is employed as anestimated drive torque of the variable displacement compressor.
 2. Amethod for estimating a drive torque of a variable displacementcompressor included in a refrigerating cycle, wherein the refrigeratingcycle comprises: a variable displacement compressor having a compressionmechanism section for compressing a refrigerant and a displacementvariable mechanism for varying a displacement of the refrigerant to becompressed by the compression mechanism section; a condenser forcondensing the refrigerant compressed by the variable displacementcompressor; a pressure reducing means for reducing pressure of therefrigerant condensed by the condenser; an evaporator for evaporatingthe refrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means, and the evaporator; and apressure detection means for detecting pressure of the refrigerant fromthe variable displacement compressor to the pressure reducing means, andwherein the method comprises: a first drive torque estimation means forcalculating a first estimated drive torque of the variable displacementcompressor based on at least a physical quantity other than pressure ofrefrigerant detected by the pressure detection means; a second drivetorque estimation means for calculating a second estimated drive torqueof the variable displacement compressor using pressure of refrigerantdetected by the pressure detection means; and a lapse of timemeasurement means for measuring lapse of time after the variabledisplacement compressor begins to compress the refrigerant, and when thelapse of time measured by the lapse of time measurement means is lessthan a predetermined time, the first estimated drive torque is employedas an estimated drive torque of the variable displacement compressor andwhen the lapse of time measured by the lapse of time measurement meansis equal to or more than the predetermined time, the second estimateddrive torque is employed as an estimated drive torque of the variabledisplacement compressor.
 3. The method for estimating a drive torque ofa variable displacement compressor as set forth in claim 2, wherein: thedisplacement variable mechanism varies the displacement of therefrigerant to be compressed by the compression mechanism section by acontrol current input from an outside; and the first drive torqueestimation means calculates the first estimated drive torque based onthe control current.
 4. The method for estimating a drive torque of avariable displacement compressor as set forth in claim 1, wherein thefirst drive torque estimation means calculates the first estimated drivetorque using the lapse of time after the variable displacementcompressor begins to compress the refrigerant and a value stored inadvance in accordance with the lapse of time.
 5. A system forcontrolling a drive source rotation speed, wherein the variabledisplacement compressor is driven by a drive source and the estimateddrive torque calculated by the method for estimating a drive torque of avariable displacement compressor as set forth in claim 1 is used tocontrol rotation speed of the drive source.
 6. A system for controllinga drive source rotation speed, comprising a refrigerating cycle having:a variable displacement compressor having a compression mechanismsection for compressing a refrigerant and a displacement variablemechanism for varying a displacement of the refrigerant to be compressedby the compression mechanism section; a condenser for condensing therefrigerant compressed by the variable displacement compressor; apressure reducing means for reducing pressure of the refrigerantcondensed by the condenser; an evaporator for evaporating therefrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means and the evaporator; and apressure detection means for detecting the pressure of the refrigerantfrom the variable displacement compressor to the pressure reducingmeans, a drive source for driving the variable displacement compressor,a lapse of time measurement means for measuring lapse of time after thevariable displacement compressor begins to compress the refrigerant, adrive torque estimation means for calculating an estimated drive torqueof the variable displacement compressor using pressure of refrigerantdetected by the pressure detection means, and a rotation speedcalculation means for calculating a target rotation speed of the drivesource using the estimated drive torque, wherein when the lapse of timemeasured by the lapse of time measurement means is less than apredetermined time, a value, which is obtained by subtracting a torquecalculated by a predetermined calculation from an estimated drive torquecalculated by the drive torque estimation means, is used as an estimateddrive torque to be used in calculation, and the estimated drive torquecalculated by the drive torque estimation means is used, as it is, incalculation when the lapse of time measured by the lapse of timemeasurement means is equal to or more than the predetermined time. 7.The system for controlling a drive source rotation speed as set forth inclaim 5, wherein the rotation speed calculation means calculates atarget idle rotation speed of the drive source.
 8. A method forestimating a drive torque of a variable displacement compressor in arefrigerating cycle, wherein the refrigerating cycle comprises: avariable displacement compressor having a compression mechanism sectionfor compressing a refrigerant and a displacement variable mechanism forvarying a displacement of the refrigerant to be compressed by thecompression mechanism section; a condenser for condensing therefrigerant compressed by the variable displacement compressor; apressure reducing means for reducing pressure of the refrigerantcondensed by the condenser; an evaporator for evaporating therefrigerant reduced in pressure by the pressure reducing means;refrigerant pipes for connecting the variable displacement compressor,the condenser, the pressure reducing means, and the evaporator; and apressure detection means for detecting pressure of refrigerant from thevariable displacement compressor to the pressure reducing means, whereinthe method comprises: a first drive torque estimation means forcalculating a first estimated drive torque of the variable displacementcompressor, which is calculated based on at least a physical quantityother than pressure of refrigerant detected by the pressure detectionmeans and gradually increases with lapse of time after the variabledisplacement compressor begins to compress the refrigerant; and a seconddrive torque estimation means for calculating a second estimated drivetorque of the variable displacement compressor using pressure ofrefrigerant detected by the pressure detection means, and the firstestimated drive-torque and the second estimated drive torque arecompared and the one with the value closer to an actual drive torque isemployed as an estimated drive torque of the variable displacementcompressor.
 9. The method for estimating a drive torque of a variabledisplacement compressor as set forth in claim 2, wherein the first drivetorque estimation means' calculates the first estimated drive torqueusing the lapse of time after the variable displacement compressorbegins to compress the refrigerant and a value stored in advance inaccordance with the lapse of time.
 10. A system for controlling a drivesource rotation speed, wherein the variable displacement compressor isdriven by a drive source and the estimated drive torque calculated bythe method for estimating a drive torque of a variable displacementcompressor as set forth in claim 2 is used to control rotation speed ofthe drive source.
 11. The system for controlling a drive source rotationspeed as set forth in claim 6, wherein the rotation speed calculationmeans calculates a target idle rotation speed of the drive source.